Optical disks as optical recording media, particularly read-only ROM (Read Only Memory) disks, are widely used around the world as package media, because a large number of replica substrates may be manufactured in a short time at low cost from one stamper by plastic injection molding.
For example, CDs (Compact Discs) and DVDs (Digital Versatile Discs) are commonly used as ROM disks for recording data such as music and images.
Conventionally, duplicated disks called pirated disks have been prepared by illegally copying recorded data of ROM disks sold as package media, and violation of copyrights is a problem.
Pirated disks are generally manufactured as duplicated disks from a stamper prepared by a mastering process based on a signal reproduced from a normal disk.
Alternatively, pirated disks are manufactured by copying a signal reproduced from a normal disk to a recordable disk.
Various methods have been proposed and studied to prevent the manufacture of pirated disks.
As one of the methods, there is known a method of adding different identifications to individual disks, for example. Using the method of adding different identifications to individual disks makes it possible to build a system in which a reproduction device reads an identification of a disk and transmits it to an external server through a network. The presence of pirated disks may be detected using such a system, because a large number of identical identifications are detected by the server when pirated disks are prepared and sold, for example. Further, pirated disk manufacturers may be specified by specifying a reproduction device having transmitted the detected identification.
However, even in the case where unique identifications are added to individual disks as described above, recording by a method preventing easy reproduction and copying using a commercially available drive is useful for protecting copyrights.
Accordingly, a recording method has been proposed in which a mark of the aforementioned identification is formed on a reflective film of a disk to provide a slight change in reflectance (see Japanese Patent No. 3454410, for example).
In the disk described in Japanese Patent No. 3454410, main data (data such as content data or management information) is recorded with a combination of pits and lands, and auxiliary data (identification) other than the main data is recorded by forming a mark providing a slight change in reflectance on a reflective film on a predetermined pit or land.
The aforementioned recording of a mark on the reflective film is performed by laser irradiation using recording power higher than reproduction laser power. Here, a change in reflectance due to the mark is so slight that there is no influence on reproduction of main data recorded with a combination of pits and lands. Specifically, auxiliary data is prevented from being reproduced in normal reproduction of the main data.
The auxiliary data itself is reproduced by providing a separate reproduction system, sampling many parts provided with such a slight change in reflectance in a reproduction signal of the main data, and determining an integrated value of these, for example.
In this case, a position on which a mark as auxiliary data should be formed is determined by a predetermined algorithm in an auxiliary data recording device and a reproduction device. Therefore, a normal reproduction device may appropriately reproduce an identification as auxiliary data, because a position on which a mark should be recorded may be specified by the same algorithm as used in recording.
Pirated disks are assumed to be prepared using a reproduction signal of a normal ROM disk. Another method is possible where a stamper is prepared by directly transferring a physical shape of a substrate of a ROM disk.
Specifically, in the method, a cover layer and a reflective film of a normal disk are separated from a substrate to expose a shape of pits and lands formed on the substrate, and the exposed irregular shape is physically transferred to duplicate a content recorded on the disk.
In the aforementioned disk described in Japanese Patent No. 3454410, an identification of an individual disk is recorded with a mark formed on a reflective film. According to this, a mark (identification) formed on a reflective film may not be transferred by the aforementioned physical transfer method in which it is necessary to separate a cover layer and a reflective film from a substrate. Therefore, it is assumed that the manufacture of pirated disks may be prevented.
However, a mark is actually recorded on a reflective film by irradiation with a relatively high power laser. Therefore, deformation corresponding to the mark on a substrate itself such as local thermal expansion may occur on the disk substrate due to heating of the recorded part when the intended mark is recorded.
In other words, a mark that should be formed only on a reflective film may also be physically transferred to a substrate, and auxiliary data may be duplicated together with main data by the physical transfer to the substrate.
This transfer will be described with reference to the following FIG. 33.
FIG. 33A shows a cross-sectional structure of an optical disk 100 having a mark formed on a reflective film as described above.
The optical disk 100 includes a reflective film 102 and a cover layer 103 formed on a substrate 101. An irregular cross-sectional shape formed between the substrate 101 and the reflective film 102 is a part on which main data is recorded with a combination of pits and lands.
As described above, a mark as auxiliary data as indicated by a symbol X is recorded on a reflective film on a predetermined pit or land. The figure shows an example where the mark X is recorded on the reflective film 102 on a predetermined land.
In the present specification, a land refers to a part optically close to a source of light incident on an irregular surface on an optical recording medium such as an optical disk, that is, a part having a shape projected to a light incidence side.
In this case, as described above, when a mark as auxiliary data is recorded, the reflective film 102 is irradiated with a relatively high power laser, and deformation due to thermal expansion or the like with the increase in temperature may occur in a place X on which the mark is formed.
A recessed dent is transferred to a surface of the substrate 101 in contact with the reflective film 102 by this deformation. Specifically, when the substrate 101 is exposed by separating the cover layer 103 and the reflective film 102 in this case, a recessed shape corresponding to a mark that should be formed only on the reflective film 102 is transferred to a surface of the substrate 101 as shown in FIG. 33B.
The recessed part transferred in this manner has a reflectance slightly decreased from that of another land. In other words, a mark as auxiliary data is directly reproduced in a replica (replicated) substrate prepared by directly transferring such a recessed shape of the substrate 101.
When a reflective film and a cover layer are stacked on such a replica substrate in the same manner as in a typical manufacturing process, a pirated disk may be manufactured in which main data and auxiliary data recorded on a normal disk are entirely copied.
In Japanese Patent Application No. 2005-205439 (an application claiming priority based on Japanese Patent Application No. 2005-30272), the present applicant has previously proposed a reproduction device, a reproduction method, a recording device, a recording method, a method of manufacturing an optical disk, and an optical disk recording medium, where reproduction in a manner such as polarity inversion different from that of a normal copy is performed on a so-called pirated optical recording medium prepared by illegal duplication even when auxiliary data for duplication prevention or detection is physically transferred as described above.